reset: core: fix reset_control_put

Commit "reset: make optional functions really optional" missed to
adjust one check in reset_control_put, causing a NULL pointer
access for optional resets.

Fixes: bb475230 "reset: make optional functions really optional"
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

drivers/reset/core.c

@@ -392,7 +392,7 @@ EXPORT_SYMBOL_GPL(__of_reset_control_get);
 
 void reset_control_put(struct reset_control *rstc)
 {
-	if (IS_ERR(rstc))
+	if (IS_ERR_OR_NULL(rstc))
 		return;
 
 	mutex_lock(&reset_list_mutex);